Transverse spin asymmetries at COMPASS: beyond Collins and Sivers effects

Understand

One of the important objectives of the COMPASS experiment (SPS, CERN) \cite{Abbon:2007pq} is the exploration of the transverse spin structure of the nucleon via spin dependent azimuthal asymmetries in single-hadron production in deep inelastic scattering of polarized leptons off transversely polarized targets.

• For this purpose a series of measurements were made in COMPASS, using 160 GeV/c longitudinally polarized muon beam and transversely polarized $^6LiD$ (in 2002, 2003 and 2004) and $NH_3$ (in 2007 and 2010) targets.
• In the past few years considerable theoretical interest and experimental efforts were focused on the study of Collins and Sivers transverse spin asymmetries.
• The experimental results obtained so far play an important role in the general understanding of the three-dimensional nature of the nucleon in terms of transverse momentum dependent parton distribution functions.